Glazing materials sometimes include one or more functional layers engineered to enhance the performance of the glazing. One important functional layer reduces transmission of infrared radiation. Infrared-rejecting functional layers are typically made of partially transparent metallized or dyed polymer film constructions that reflect or absorb unwanted solar radiation. References describing such functional layers include U.S. Pat. Nos. 4,590,118, 4,639,069 and 4,799,745.
Infrared-rejecting functional layers are of particular interest in vehicular safety glazing. Conventional vehicular safety glazing is a laminate of two rigid layers, typically glass, and an anti-lacerative mechanical energy-absorbing interlayer, typically plasticized polyvinyl butyral (“PVB”). The glazing is prepared by placing the PVB layer between the glass layers, eliminating air from the engaging surfaces, and then subjecting the assembly to elevated temperature and pressure in an autoclave to fusion bond the PVB and glass into an optically clear structure. The resulting safety glazing can be used, for example, in an automobile, airplane, train or other vehicle.
When infrared-rejecting functional layers are used in a windshield, regulations require that the completed laminate should have a luminous transmittance (measured according to ASTM E308) of at least 70%. When used in other vehicular glazing structures, such as side windows, backlights or sunroofs, or in other applications such as architectural glazing, there are typically no regulatory limits on the level of visible transmission. In any event, the laminate preferably should reject a substantial portion of solar radiation outside the visible portion of the spectrum in a wavelength region of interest, e.g., at least 50% of the light in a band at least 100 nm wide between about 700 nm and about 2,000 nm.
FIG. 1A shows a conventional pre-laminate structure 10 that can be bonded to one or more glass sheets to make a vehicular safety glazing laminate. The pre-laminate 10 includes a reflective functional layer 12 having a flexible plastic support layer 14 and a metallized layer 16. The functional layer 12 is bonded on at least one side to at least one layer 18 of PVB. Optionally, the functional layer 12 can be bonded to a second layer 20 of PVB. One or the other or both of the PVB layers 18, 20 can include additional performance enhancing layers. For example, the PVB layer 20 may optionally include a shade band layer 22.
Referring to FIG. 1B, pre-laminate 10 is conventionally matched with at least one, and preferably two sheets of glass 30, 32 to form a vehicular safety glazing laminate 34. To bond pre-laminate 10 to glass sheets 30, 32, pre-laminate 10 and sheets 30, 32 are placed together and heated to cause the PVB layers 18, 20 and the functional layer 12 to conform to the contours of the glass sheets 30, 32. This bonding and heating process is typically carried out using a vacuum de-airing method or a nip roll method. In the vacuum de-airing method, the entire laminate is placed into a bag connected to a vacuum system (or a flexible sealing band or ring is placed around the edge of the laminate and connected to a vacuum system) and a vacuum is drawn while the laminate is heated, thereby removing air from the glass PVB interface(s) and temporarily bonding the glass to the PVB. The nip roll method uses one or more pressure roller devices, commonly called nip rolls, which apply pressure to the laminate to de-air and promote bonding between the layers. For either the vacuum de-airing method or the nip roll method, the lamination process typically is completed by heating the laminate assembly in an autoclave under pressure. Compared to the vacuum de-airing methods, the nip roll method requires fewer manual steps and allows the laminates to be assembled more quickly. For at least these reasons, the nip roll method is a preferred lamination method for many automotive glazing manufacturers.